A drum filter of the pipe machine type comprises a rotary drum partially submerged in a tank of pulp slurry. Typically, the drum has axially extending filtrate channels spaced about its peripheral surface defined by ribs and covered by a filter screen. The surface filtrate channels communicate with an external source of subatmospheric pressure, or suction, through drainage pipes, an annular valve housing mounted centrally within the discharge end of the drum, a stationary vacuum breaker valve member seated within the valve housing and extending therefrom, and a discharge elbow connected to the outlet end of the valve member. The stationary valve member has a valve closure segment which blocks off a section of multiple discharge ports in the valve housing to control the application of subatmospheric pressure to the connected drainage pipes and surface filtrate channels.
As the drum rotates about its axis with suction applied, the screen rotates through the pulp slurry and collects a wet mat or "cake" of fibres from the slurry. As the screen emerges from the tank, filtrate is drawn from the mat through the screen and filtrate channels into the drainage pipes, and from there through the valve housing and into the valve member and discharge elbow to remove the filtrate from the drum. During rotation of the drum, the stationary valve closure segment cuts off suction to the filtrate channels in a segment of the drum surface, thereby enabling removal of the pulp mat from the screen surface, usually with the aid of a doctor device.
Rotary drum filters of the described pipe machine type are shown, for example, in U.S. Pat. No. 3,363,774 to Luthi and U.S. Pat. No. 4,383,877 to LaValley.
Typically, the stationary valve member for such a drum filter, partially shown in FIG. 7 of the Luthi patent, has a cylindrical valve plug at its inlet end which is seated within the valve housing. A conically tapered valve closure segment extends rearwardly from the plug to cover a portion of the valve housing outlet ports to block them from the source of suction. A large central shaft extends rearwardly from the plug and outwardly beyond the discharge end of the drum, connecting with an annular flange and sealing rim at the outlet end of the valve member, such outlet end portion not being shown in the Luthi patent. Usually, a hollow generally cylindrical drive trunnion or shaft connected to the drum surrounds the shaft portion of the valve member to define a portion of the filtrate discharge passage leading from the drum. The outlet end of the valve member joins an inlet end of the discharge elbow at respective flanges, bolted together. The outlet end of the elbow, in turn, connects to a suction pipe leading to the source of subatmospheric pressure. The drive trunnion or shaft is enclosed within a stationary drive housing, shown in the vicinity of item 24 in FIG. 1 of the Luthi patent. The drive housing houses the drum drive means, typically a worm gear or chain drive.
The drive housing typically is part of the drum support structure and serves as a support for the valve member. A flange on the discharge elbow bolts to the valve flange to form the valve-elbow assembly. Ears on the elbow flange bolt to the drive housing to support the valve-elbow assembly on the drive housing. However, seating of the valve closure segment precisely within the drum's valve housing is critical. Therefore means must be provided for adjusting the position of the elbow flange both axially and transversely of the valve member on the drive housing to achieve proper seating of the segment. Such means usually include both axial and radial adjustment bolts acting between the elbow flange and the drive housing.
Proper seating of the valve closure segment is complicated by the fact that the valve member and discharge elbow must be securely bolted together at their flanges when the seating adjustment is made because the elbow flange connects the valve member to the drive housing. When the elbow is connected to the valve member, access to the valve housing and segment end of the valve member is extremely limited, making accurate seating difficult and tedious. Seating can only be accomplished through trial and error using a feeler gauge affixed to a long stick inserted through a small inspection port in the elbow.
Rotational adjustment of the valve closure segment relative to the valve housing is also important to ensure that the drum surface is cut off from suction to enable removal of the mat at a precise angular position of such surface during drum rotation. However, with the valve member supported from the drive housing by the elbow flange, precise rotational adjustment of the valve segment is also difficult and tedious because of the access problems previously described. In addition, many types of prior valve-discharge elbow assemblies do not accomodate rotational valve adjustment at all, at least not without their complete disassembly.
From the foregoing, it will be apparent that there is a need for an improved method and means for seating and rotationally adjusting the valve closure segment of a vacuum breaker valve within the valve housing of a rotary drum filter. This need, in turn, suggests the need for an improved method and means for mounting the valve member and discharge elbow to the drive housing of a rotary drum filter that will simplify and improve the accuracy of seating and rotationally adjusting the valve closure segment in the valve housing.
In view of the foregoing needs, primary objectives of the present invention are to provide:
1. an improved method and means for seating and rotationally adjusting the valve member in the valve housing of a rotary drum filter; and
2. an improved method and means for mounting a valve-discharge elbow assembly that simplifies, speeds up, and renders more accurate, the seating and rotational adjustment of the valve member in the valve housing of a rotary drum filter as compared to prior such methods and means.
More specific objectives of the present invention include the provision of an improved method and means for mounting a valve-discharge elbow assembly to a rotary drum filter which enable (a) seating of the valve member while the discharge elbow is removed from the valve member, (b) rotational adjustment of the valve member with the elbow either connected to or disconnected from the valve member as desired; (c) rotational adjustment of the valve member without the need for access to the valve housing and without the use of a feeler gauge; (d) rotational adjustment of the valve member without the need for reseating it; and (e) removal of the discharge elbow from the valve-elbow assembly for valve inspection or adjustment without the need for reseating or readjusting the valve upon reassembly of the valve and elbow.